Got black image when decode base64

Question

When I decode a base64 encoded cropped face image, it goes black and the data corrupts.

This is the piece of code:

def create_learn_msg(db_name, person_name, last_location, images, labels):
    json_string = {}
    cv2.imwrite('%s/%s.png' % ("faces/", "original-image"), images[1])
    print(type(images[1]))  # <type 'numpy.ndarray'>
    image_string = images[1].tostring()
    encode_string = base64.b64encode(image_string)
    # Decode test
    decode_string = base64.b64decode(encode_string)
    decode_image = numpy.fromstring(decode_string, dtype=numpy.uint8)

    print(type(decode_image))  # <type 'numpy.ndarray'>
    cv2.imwrite('%s/%s.png' % ("faces/", "decode-image"), decode_image)

    json_string['data'] = {'type': "learn", 'db_name': db_name, 'person_name': person_name,
                           'last_location': last_location, 'image1': base64.b64encode(images[0]),
                           'image2': base64.b64encode(images[1]), 'label1': labels[0], 'label2': labels[1]}

    return json.dumps(json_string)

some lines were missing, i fixed the code. now whats your idea? — Farshid616, Jan 15 '18 at 09:25
This looks more like something that could work now. Are you sure the original image is of `uint8` data type? I suggest you follow tripleee's advice above. — MB-F, Jan 15 '18 at 09:30
yes i'm sure, i try @tripleee solution but every thing is the same — Farshid616, Jan 15 '18 at 10:28

score 2 · Accepted Answer · edited Jul 31 '22 at 09:40

I found the solution, we're using the OpenCV image so we should add cv2.imencode before base64 encoding and cv2.imdecode after base64 decoding as following:

retval, image_string = cv2.imencode('.png', images[1])
encode_string = base64.b64encode(image_string)
decode_string = base64.b64decode(encode_string)
decode_image = numpy.fromstring(decode_string, dtype=numpy.uint8)
original_image = cv2.imdecode(decode_image, 1)

score 1 · Answer 2 · answered Jan 15 '18 at 09:29

1

this cv2.imwrite('%s/%s.png' % ("faces/", "decode-image"), q) does not decode the base64 encoded data

in Convert base64 String to an Image that's compatible with OpenCV is code for this :

# reconstruct image as an numpy array
img = imread(io.BytesIO(base64.b64decode(b64_string)))

# show image
plt.figure()
plt.imshow(img, cmap="gray")

# finally convert RGB image to BGR for opencv
# and save result
cv2_img = cv2.cvtColor(img, cv2.COLOR_RGB2BGR)
cv2.imwrite("reconstructed.jpg", cv2_img)
plt.show()

( https://docs.opencv.org/2.4/modules/highgui/doc/reading_and_writing_images_and_video.html )

answered Jan 15 '18 at 09:29

ralf htp

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Did you write that answer before the question was edited? It does not quite match now... – MB-F Jan 15 '18 at 09:31
yes, wrote it before. i think now that the question is edited it could work and this answer is obsolete ... – ralf htp Jan 15 '18 at 09:33

Got black image when decode base64

2 Answers2